Interference with a Tuning Fork
用调谐叉的干涉
If you strike a tuning fork and rotate it next to your ear, you will note that the sound alternates between
loud and soft
as you rotate through the angles where the interference is constructive and destructive. It is challenging to visualize this in a diagram because of the large difference in scale between the tuning fork and the wavelengths of the sound produced. A tuning fork to produce equal tempered middle-C (C4, 261.6Hz) would have a dimension of a few centimeters, but the sound wavelength at room temperature would be about 1.3 m or over four feet.
如果你敲击一个调谐叉并将其旋转到你的耳边，你会注意到当旋转通过干涉 constructive 和 destructive 的角度时，声音会交替地变得响亮和微弱。由于调谐叉与声音波长的尺度差异很大，很难在图中直观地表现这一现象。要产生等 tempered 中音 C（C4，261.6Hz）的调谐叉，其尺寸约为几厘米，但在室温下，声音的波长约为1.3米或超过四英尺。
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This is an attempt to qualitatively visualize the interference from a binary source using a photo of the interference pattern in a ripple tank with a double vibrator. That photo is superimposed on a sketch of a tuning fork in the hope that it might give some insight about the nature of interference in waves from a double source. But the scale here is profoundly different: the separation of the two ripple tank wave sources is several wavelengths, whereas the separation of the two tines of the C-tuning fork is maybe 1/50th of the wavelength. This pattern would suggest several minima of loudness, whereas the tuning fork gives four minima at 45° from the plane of the two tines when rotated.
这是一种尝试定性地可视化二源干涉的图像，使用了水槽中双振动器产生的干涉图案照片。该照片叠加在一把调谐叉的草图上，希望借此对双源波干涉的本质有所启发。但这里的尺度差异非常显著：两个水槽波源之间的距离是几个波长，而C调谐叉两个音叉齿之间的距离可能只有波长的1/50。这种图案会显示出几个响度的极小值，而当调谐叉旋转时，从两个音叉齿平面的45°方向会出现四个响度极小值。
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Animations of the interference patterns with single and multiple sources may be found at Dan Russell's site at Penn State. The pattern at right is from the animation of a lateral quadrupole source. This is the best approximation of the interference of the tuning fork since the two tines of the fork are out of phase, and Russell notes that two opposite phase dipoles make up a lateral quadrupole source. This diagram gets closer to what you experience by rotating the tuning fork by your ear, but the problem of scale is still present since the sound wavelength for the C tuning fork is fifty times the size of the physical vibrator.
单源和多源干涉图样的动画可以在宾夕法尼亚州立大学的Dan Russell网站上找到。右边的图样来自一个横向四极源的动画。这是调谐叉干涉的最好近似，因为叉子的两个叉臂相位相反，而Russell指出，两个相位相反的偶极子构成一个横向四极源。这个图样通过将调谐叉贴近耳朵旋转，更接近你实际听到的声波，但比例问题仍然存在，因为C调调谐叉的声波波长是物理振动器尺寸的五十倍。 | 
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 | This diagram shows that Russell's lateral quadrupole gives equal intensities at 90°. But with the tuning fork, your ear tells you that the maxima in the plane of the two tines is significantly stronger than the maxima perpendicular to that plane.
此图显示，Russell的横向四极子在90°处给出相等的强度。但使用音叉时，你的耳朵会告诉你，在两个叉片所在平面内的最大值明显强于垂直于该平面的最大值。 |
Each tine of the fork produces a pressure wave which travels outward at the speed of sound. One part of the wave has a pressure higher than atmospheric pressure, another lower. At some angles the high pressure areas of the two waves coincide and you hear a louder sound. At other angles, the high pressure part of one wave coincides with the low pressure part of the other.
叉子的每一次振动都会产生一个压力波，以声速向外传播。波的一部分压力高于大气压，另一部分则低于大气压。在某些角度上，两个波的高压区会重合，你就会听到更响的声音。在其他角度上，一个波的高压部分会与另一个波的低压部分重合。
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Index
Traveling wave concepts
Sound propagation concepts
索引 旅行波概念 声波传播概念 |
